Is it correct or incorrect for a Java JAR to contain its own dependencies?
- by 4herpsand7derpsago
I guess this is a two-part question. I am trying to write my own Ant task (MyFirstTask) that can be used in other project's build.xml buildfiles. To do this, I need to compile and package my Ant task inside its own JAR. Because this Ant task that I have written is fairly complicated, it has about 20 dependencies (other JAR files), such as using XStream for OX-mapping, Guice for DI, etc.
I am currently writing the package task in the build.xml file inside the MyFirstTask project (the buildfile that will package myfirsttask.jar, which is the reusable Ant task).
I am suddenly realizing that I don't fully understand the intention of a Java JAR. Is it that a JAR should not contain dependencies, and leave it to the runtime configuration (the app container, the runtime environment, etc.) to supply it with the dependencies it needs? I would assume if this is the case, an executable JAR is an exception to the rule, yes?
Or, is it the intention for Java JARs to also include their dependencies?
Either way, I don't want to be forcing my users to be copying-n-pasting 25+ JARs into their Ant libs; that's just cruel. I like the way WAR files are set up, where the classpath for dependencies is defined under the classes/ directory.
I guess, ultimately, I'd like my JAR structure to look like:
myfirsttask.jar/
com/ --> the root package of my compiled binaries
config/ --> config files, XML, XSD, etc.
classes/ --> all dependencies, guice-3.0.jar, xstream-1.4.3.jar, etc.
META-INF/
MANIFEST.MF
I assume that in order to accomplish this (and get the runtime classpath to also look into the classes/ directory), I'll need to modify the MANIFEST.MF somehow (I know there's a manifest attribute called ClassPath, I believe?). I'm just having a tough time putting everything together, and have a looming/lingering question about the very intent of JARs to begin with.
Can someone please confirm whether Oracle intends for JARs to contain their dependencies or not? And, either way, what I would have to do in the manifest (or anywhere else) to make sure that, at runtime, the classpath can find the dependencies stored under the classes/ directory? Thanks in advance!
